The present invention relates to an improved valve rotating device of the garter spring type.
Valve rotators utilizing a garter spring for effecting valve rotation are known. Typically, a device of the general type contemplated is disclosed in U.S. Pat. No. 3,421,734 issued to Updike et al. and dated Jan. 14, 1969, the disclosure of which is incorporated herein in its entirety by reference thereto. Such rotator devices locate the garter spring between a spring washer in circular contact with the garter spring and valve spring retainer means including an annular pocket dimensioned for limited interference contact between the garter spring and the spring washer. For example, in the Updike patent, there is provided a garter spring 30, coacting between a spring washer 33 and an annular pocket 19 in the body 10. The body 10 having a taper 13 engages the valve stem 24 having a mating taper 27 to lock the body 10 to the valve stem and retain and transmit the tension of the valve spring 48 to the valve.
Other garter spring type valve rotating devices are shown in the U.S. Pat. to Orent, No. 3,537,325 dated Nov. 3, 1970 and the U.S. Pat. to Schonlau et al., No. 3,890,943 dated June 24, 1975. The structures of these devices may also be improved in accordance with the present invention.
It has been found that with the side-loaded garter spring type valve rotating devices, the springs are subject to dynamic overloading and excitation by certain resonant frequencies. They are also subjected to high tensile stresses due to the twisting of the garter spring brought about by the uneven spacing between the coils at the inner and outer pocket diameter as hereinafter more particularly explained. The inner coils being more closely spaced make contact and the outer coils remain free to move tangentially when the garter spring tilts thus creating a distortion of the coil shape as the spring collapses. These additional loads can increase garter spring stresses significantly beyond the design loads and under some operating conditions, can lead to short term fatigue failures.
For example, in the Updike patent, the garter spring while provided with a retainer 32 the purpose of which seems to be to aid maintaining the shape of the garter spring 30 during assembly, is still subject to stresses, fatigue and the like mentioned above.